A growing segment of the semiconductor business is high voltage/high power devices and integrated circuits. A critical element in this business is the power MOSFET. Power MOSFETs have many diverse applications in automotive, communications, consumer, data processing, industrial and military markets. For example, power MOSFETs may be used as drivers for motors, lamps, or displays. Most power MOSFETs are built in silicon. However, the performance of power MOSFETs built in silicon are already close to their theoretical limits.
A common device structure for power MOSFETs is a vertical structure. In the vertical device (100) of FIG. 1, the gate (102) and source (104) terminals are at the top surface and the drain terminal (106) is at the bottom. The carrier flow path is from the top source electrode (104), through the lateral channel (114)underneath the gate electrode (102), then vertically through the drift region (108) and n+ substrate (110), to the drain electrode (106). In silicon, the p-well (112) is typically 2-5 microns deep, and the drift region (108) is typically 5-30 microns deep for devices with breakdown voltage ratings in the 50-400 V range. This device structure is used primarily for discrete devices.